Multi-Interface-Induced Thermal Conductivity Reduction and Thermoelectric Performance Improvement in a Cu–Ni Alloy

Abstract

A Cu–Ni-based alloy with a high power factor is a commercially utilized metallic thermocouple material. However, the high thermal conductivity has been a major limitation to achieving thermoelectric performance in semiconductor materials. Herein, this work presents a 76.1% reduced thermal conductivity (∼7.7 W m–1 K–1) in Cu70Ni30, which is one of the lowest reported values in the literature. Such suppression of thermal conductivity can be attributed to the varied frequency phonon scattering by the interfacial potential barrier, built from micron-scale defects formed via sintering melt-spun ribbons. However, the defects simultaneously reduce the charge carrier concentration, mobility, and thus the electrical conductivity. The lowest thermal conductivity leads to the highest zT and ZT avg in the sample sintered at 673 K under 15 MPa. The values are 0.24 (@573 K) and 0.15 (323–573 K), respectively, which are 130.3 and 140.0% higher than the values of the pristine counterpart. Our work demonstrates that improved thermoelectric performance in Cu–Ni-based alloys can be obtained by creating various interfacial defects even at micron scales, which paves the way to suppress thermal conductivity largely in metallic thermoelectric materials via melt-spinning (MS) and spark plasma sintering (SPS) synthesis.

Precision Interface Engineering of CuNi Alloys by Powder ALD Toward Better Thermoelectric Performance

“…However, it is important to consider that CuNi alloys with finer grains and a more optimized composition (such as Cu 55 Ni 45 ) and doping (with Se) have the potential to yield even higher initial zT values. Therefore, it is reasonable to anticipate that by employing the same pristine material conditions reported in studies like Yuan et al.’s, or others, [ 38–44 ] further enhancements in zT values are potentially achievable.…”

“…For the sample modified with Z44/A11/Z44 multilayers, due to decoupling thermoelectric parameters by ALD, a maximum figure of merit (zT) of 0.22 was achieved at 673 K, ≈128% higher than that of pristine CuNi and is a bit higher than the previously reported vaules [38][39][40][41][42][43][44] (Figure 2).…”

“…In high cycle number coating (>50 cycles), the multilayer coatings maintained the high PF while significantly reducing the thermal conductivity. For the sample modified with Z44/A11/Z44 multilayers, due to decoupling thermoelectric parameters by ALD, a maximum figure of merit ( zT ) of 0.22 was achieved at 673 K, ≈128% higher than that of pristine CuNi and is a bit higher than the previously reported vaules [ 38–44 ] ( Figure ).…”

“…Comparison of temperature-dependent zT among other optimized CuNi works. [[38][39][40][41][42][43][44]…”

Integration of an Axially Continuous Graphene with Functional Metals for High‐Temperature Electrical Conductors

“…[26] Despite the improved thermal stability, long-term operation of the Ni-coated Cu wires in elevated temperatures, e.g., up to 450 °C in aerospace turbine engines, [6] is infeasible due to the interdiffusion between Ni and Cu. [26][27][28] Such alloying process results in a sharp decrease in both electrical conductivity and charge-carrying capacity, for example, Cu70Ni30 specimen shows a ≈ 2.3 × 10 4 S cm −1 electrical conductivity after spark plasma sintering using melt-spun Cu70Ni30 ribbons [29] while pure copper has a 58.1 × 10 4 S cm −1 . In addition, alloying of Ni and Cu significantly compromises the oxidation resistance of the Ni shell [12,30] due to migration of Cu atoms into the shell.…”